U.S. patent number 9,659,754 [Application Number 14/071,717] was granted by the patent office on 2017-05-23 for plasma processing apparatus and plasma processing method.
This patent grant is currently assigned to TOKYO ELECTRON LIMITED. The grantee listed for this patent is TOKYO ELECTRON LIMITED. Invention is credited to Naoki Matsumoto, Yoshio Susa, Peter L. G. Ventzek, Jun Yoshikawa.
United States Patent |
9,659,754 |
Yoshikawa , et al. |
May 23, 2017 |
Plasma processing apparatus and plasma processing method
Abstract
The present disclosure provides a plasma processing apparatus,
including: a processing chamber; an oscillator configured to output
high-frequency power; a power supply unit configured to supply the
high-frequency power from a specific plasma generating location
into the processing chamber; a magnetic field forming unit provided
outside the processing chamber and configured to forming a magnetic
field at least at the specific plasma generating location; and a
control unit configured to control the magnetic field formed by the
magnetic field forming unit such that a relationship between an
electron collision frequency fe of plasma generated in the
processing chamber and a cyclotron frequency fc is fc>fe.
Inventors: |
Yoshikawa; Jun (Miyagi,
JP), Susa; Yoshio (Miyagi, JP), Matsumoto;
Naoki (Miyagi, JP), Ventzek; Peter L. G. (Austin,
TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
TOKYO ELECTRON LIMITED |
Tokyo |
N/A |
JP |
|
|
Assignee: |
TOKYO ELECTRON LIMITED (Tokyo,
JP)
|
Family
ID: |
50621403 |
Appl.
No.: |
14/071,717 |
Filed: |
November 5, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140124478 A1 |
May 8, 2014 |
|
Foreign Application Priority Data
|
|
|
|
|
Nov 6, 2012 [JP] |
|
|
2012-244348 |
Aug 2, 2013 [JP] |
|
|
2013-161875 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J
37/32669 (20130101); H01J 37/32678 (20130101); H01J
37/3266 (20130101) |
Current International
Class: |
C23C
16/00 (20060101); H01J 37/32 (20060101); H01L
21/306 (20060101); C23F 1/00 (20060101) |
Field of
Search: |
;156/345.42
;118/723MR,723MA,723AN ;315/111.41 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Dhingra; Rakesh
Attorney, Agent or Firm: Rothwell, Figg, Ernst &
Manbeck, P.C.
Claims
What is claimed is:
1. A microwave plasma processing apparatus comprising: a processing
chamber including a susceptor configured to dispose a substrate to
be processed; an oscillator configured to output high-frequency
power; a power supply unit including a transmission plate and
configured to supply the high-frequency power to a specific plasma
generating location in the processing chamber, the transmission
plate including a concave portion of which a center portion is
formed at an outer peripheral side of a bottom surface of the
transmission plate of the power supply unit; a magnetic field
forming unit provided outside the processing chamber near an outer
peripheral portion or a lateral portion of the transmission plate
and configured to form a magnetic field in a perpendicular
direction with respect to the susceptor at least at the specific
plasma generating location including an area near the concave
portion of the transmission plate of the power supply unit; and a
control unit programmed to control a pressure in the processing
chamber to be 50 mTorr (6.66 Pa) or less and an intensity of the
magnetic field formed in the perpendicular direction with respect
to the susceptor by the magnetic field forming unit to be 1 G to 50
G (10.sup.-4 T to 50.sup.-3 T) such that a relationship between an
electron collision frequency fe of plasma generated in the
processing chamber and a cyclotron frequency fc is fc>fe in
order to move an area where an electron density of the plasma is
high from a center side to an outer peripheral side in the
processing chamber below the concave portion, wherein the power
supply unit further includes a radial line slot antenna unit
disposed above the transmission plate and a slow-wave member
disposed on a top of the radial line slot antenna unit, wherein the
concave portion is located at a position that is 50% or more spaced
from a center of the processing chamber.
2. The plasma processing apparatus of claim 1, wherein the magnetic
field forming unit is provided on an outer peripheral portion or a
lateral portion of the power supply unit provided at a ceiling of
the processing chamber.
3. The plasma processing apparatus of claim 1, wherein the specific
plasma generating location is provided at a location of 50% or more
spaced from a center location of the processing chamber with
respect to a diameter of the processing chamber in the power supply
unit provided at a ceiling of the processing chamber.
4. The plasma processing apparatus of claim 3, wherein the specific
plasma generating location is formed outside the peripheral portion
of an object to be processed that is placed in the processing
chamber.
5. The plasma processing apparatus of claim 1, wherein a gap
between a ceiling of the processing chamber and the placed object
to be processed is set such that the magnetic field formed by the
magnetic field forming unit does not reach the placed object to be
processed.
6. The plasma processing apparatus of claim 1, wherein the gas
introduced into the processing chamber is argon gas, and the
control unit controls an electron temperature of plasma generated
in the processing chamber to be 0.5 eV to 5 eV.
7. The plasma processing apparatus of claim 1, wherein the control
unit switches ON and OFF of application of the magnetic field in
time division control, and pulse-controls the magnetic field.
8. A microwave plasma processing apparatus, comprising: a
processing chamber including a susceptor for an object to be
processed and configured to be supplied with gas to generate plasma
in the processing chamber; a magnetic field forming unit provided
outside the processing chamber and configured to form a magnetic
field in a direction perpendicular to the object to be processed
that is placed in the processing chamber; an oscillator configured
to output high-frequency power; a radial line slot antenna unit
including a transmission plate provided in the processing chamber
and configured to supply the high-frequency power output by the
oscillator to the processing chamber, the transmission plate of the
antenna unit including a concave portion of which a center portion
is formed at an outer peripheral side of a bottom surface of the
transmission plate such that the magnetic field forming unit also
forms the magnetic field at an area near the concave portion of the
transmission plate of the antenna unit; and a control unit
programmed to control a pressure in the processing chamber to be 20
mT to 200 mT (2.67 Pa to 26.7 Pa) and an intensity of the magnetic
field formed in a direction perpendicular to the susceptor by the
magnetic field forming unit to be 1 G to 50 G (10.sup.-4 T to
50.sup.-3 T) such that a relationship between an electron collision
frequency fe of plasma generated in the processing chamber and a
cyclotron frequency fc is fc>fe in order to move an area where
an electron density of the plasma is high from a center side to an
outer peripheral side in the processing chamber below the concave
portion, wherein the radial line slot antenna unit further includes
a slow-wave member disposed on a top of the antenna unit and the
radial line slot antenna is disposed above the transmission plate,
wherein the concave portion is located at a position that is 50% or
more spaced from a center of the processing chamber.
9. A microwave plasma processing method, comprising: providing a
power supply unit including a radial line slot antenna, a slow-wave
member and a transmission plate, the radial line slot antenna being
disposed above the transmission plate and the slow-wave member
being disposed on the radial line slot antenna, and the
transmission plate including a concave portion of which a center
portion is formed at an outer peripheral side of a bottom surface
of the transmission plate; supplying high-frequency power generated
from the power supply unit to a specific plasma generating location
in a processing chamber where a substrate to be processed is
disposed; forming a magnetic field in a perpendicular direction
with respect to the substrate disposed on a susceptor at least at
the specific plasma generating location including an area near the
concave portion of the transmission plate of the power supply unit
in the processing chamber by a magnet provided outside the
processing chamber; and controlling a pressure in the processing
chamber to be 50 mTorr (6.66 Pa) or less and an intensity of the
magnetic field formed in a perpendicular direction with respect to
the substrate disposed on a susceptor to be 1 G to 50 G (10.sup.-4
T to 50.sup.-3 T) such that a relationship between an electron
collision frequency fe of plasma generated in the processing
chamber and a cyclotron frequency fc is fc>fe in order to move
an area where an electron density of the plasma is high from a
center side to an outer peripheral side in the processing chamber
below the concave portion, wherein the concave portion is located
at a position that is 50% or more spaced from a center of the
processing chamber.
10. The plasma processing method of claim 9, wherein the
controlling of the magnetic field includes switching ON and OFF of
application of the magnetic field in time division and
pulse-controlling the magnetic field.
11. The plasma processing method of claim 9, wherein the specific
plasma generating location is around just below a transmission
plate serving as a dielectric window passing the high-frequency
power and a level of electron density of plasma just below the
transmission plate is higher than a level of a cutoff density of
the high-frequency power.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on and claims priority from Japanese
Patent Application Nos. 2012-244348 and 2013-161875, filed on Nov.
6, 2012 and Aug. 2, 2013, respectively, with the Japan Patent
Office, the disclosures of which are incorporated herein in their
entireties by reference.
TECHNICAL FIELD
The present disclosure relates to a plasma processing apparatus and
a plasma processing method.
BACKGROUND
A plasma processing apparatus such as a radial line slot antenna
apparatus, or the like generates plasma and performs minute
processing on a processed body such as a wafer or a substrate by
the action of the plasma, thereby manufacturing a semiconductor
device. In the plasma processing apparatus, it is important to
uniformly generate plasma. In particular, in recent years,
minuteness has been in progress due to a request for high
integration and rapidness of an LSI. Further, the processed body is
enlarged. Under the circumstances, uniformity of plasma becomes
more important in order to successfully microfabricate the
processed body.
Therefore, a radial line slot antenna apparatus is proposed, which
has a mechanism for suppressing damage of an element by improving
electron density or uniformity of plasma (see, for example,
International Publication No. WO2008/108213). According to
International Publication No. WO2008/108213, a magnetic field
forming portion is formed at an upper side of an antenna for
introducing a microwave, which is provided in the radial line slot
antenna apparatus, and a plasma feature of gas generated in a
processing container by the microwave is controlled by a magnetic
field formed by the magnetic field forming portion.
SUMMARY
The present disclosure provides a plasma processing apparatus
including: a processing chamber; an oscillator configured to output
high-frequency power; a power supply unit configured to supply the
high-frequency power from a specific plasma generating location
into the processing chamber; a magnetic field forming unit provided
outside the processing chamber and configured to form a magnetic
field at least at the specific plasma generating location; and a
control unit configured to control the magnetic field formed by the
magnetic field forming unit such that a relationship between an
electron collision frequency fe of plasma generated in the
processing chamber and a cyclotron frequency fc is fc>fe.
The foregoing summary is illustrative only and is not intended to
be in any way limiting. In addition to the illustrative aspects,
embodiments, and features described above, further aspects,
embodiments, and features will become apparent by reference to the
drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal cross-sectional view of a radial line slot
antenna apparatus according to a first exemplary embodiment.
FIG. 2 is a plan view of an antenna according to the first
exemplary embodiment.
FIG. 3 is a diagram for describing a slot location and electron
density of plasma according to the first exemplary embodiment.
FIGS. 4A-4B are diagrams illustrating a magnetic field and an
electron density distribution of plasma according to the first
exemplary embodiment.
FIG. 5 is a diagram illustrating an electron collision frequency of
plasma and a cyclotron frequency according to the first exemplary
embodiment and a second exemplary embodiment.
FIG. 6 is a diagram illustrating an intensity distribution of a
magnetic field used in a simulation of controlling plasma by the
magnetic field according to the first exemplary embodiment.
FIGS. 7A-7D are diagrams illustrating a simulation result of the
electron density distribution of plasma by a vertical magnetic
field according to the first exemplary embodiment.
FIG. 8 is a diagram illustrating controllability of a plasma
distribution by the vertical magnetic field according to the first
exemplary embodiment.
FIGS. 9A-9B are diagrams illustrating a simulation result of the
electron density distribution of plasma by a transverse magnetic
field according to the first exemplary embodiment.
FIG. 10 is a diagram illustrating a simulation result of the
electron density distribution of plasma by a pulse type magnetic
field according to the first exemplary embodiment.
FIG. 11 is a longitudinal cross-sectional view illustrating an
antenna unit of a radial line slot antenna apparatus according to a
second exemplary embodiment.
FIG. 12 is a diagram illustrating a magnetic field formed in the
second exemplary embodiment.
FIG. 13 is a diagram illustrating a state of the magnetic field
according to the second exemplary embodiment by a contour line.
FIG. 14 is a diagram illustrating electron density and an electron
temperature in the second exemplary embodiment by the contour
line.
FIGS. 15A-15D are diagrams illustrating the electron density and
the electron temperature in the second exemplary embodiment.
FIG. 16 is a diagram illustrating electron density and an electron
temperature depending on a power output ratio from a plasma
generating location in the second exemplary embodiment by the
contour line (the magnetic field is not present).
FIG. 17 is a diagram illustrating the electron density and the
electron temperature depending on the power output ratio from the
plasma generating location in the second exemplary embodiment by
the contour line (the magnetic field is present).
FIG. 18 is another diagram illustrating the electron density and
the electron temperature depending on the power output ratio from
the plasma generating location in the second exemplary embodiment
by the contour line (the magnetic field is present).
FIGS. 19A-19D are diagrams illustrating the electron density
depending on the power output ratio from the plasma generating
location in the second exemplary embodiment (the magnetic field is
present).
FIGS. 20A-20D are diagrams illustrating the electron temperature
depending on the power output ratio from the plasma generating
location in the second exemplary embodiment (the magnetic field is
present).
FIGS. 21A-21C are diagrams illustrating a layout of magnets and a
magnetic field generation example in the second exemplary
embodiment.
FIG. 22 is a diagram illustrating a relationship between a plasma
generating location and an etching rate in a process using the
magnets of FIGS. 21A-21C.
FIG. 23 is a diagram illustrating pressure dependence of the
etching rate in the process using the magnets of FIGS. 21A-21C.
DETAILED DESCRIPTION
In the following detailed description, reference is made to the
accompanying drawing, which form a part hereof. The illustrative
embodiments described in the detailed description, drawing, and
claims are not meant to be limiting. Other embodiments may be
utilized, and other changes may be made, without departing from the
spirit or scope of the subject matter presented here.
In International Publication No. WO2008/108213, since the location
of a slot or an applied magnetic field is not optimized, a problem
that uniformity of plasma is inclined in a radius direction of an
object to be processed is not solved.
In particular, under a low-pressure condition of 50 mTorr (6.66 Pa)
or less, electron density of plasma at the center side of a plasma
processing apparatus tends to be higher than the electron density
of plasma at an outer peripheral side thereof and it is more
difficult to control plasma by an inclination of the electron
density of plasma toward the center side.
In order to solve the problem, the present disclosure provides a
plasma processing apparatus and a plasma processing method that can
improve controllability of a plasma distribution by optimizing an
applied magnetic field.
In order to solve the problem, a plasma processing apparatus
according to an exemplary embodiment of the present disclosure
includes: a processing chamber; an oscillator configured to output
high-frequency power; a power supply unit configured to supply the
high-frequency power from a specific plasma generating location
into the processing chamber; a magnetic field forming unit provided
outside the processing chamber and configured to form a magnetic
field at least at the specific plasma generating location; and a
control unit configured to control the magnetic field formed by the
magnetic field forming unit such that a relationship between an
electron collision frequency fe of plasma generated in the
processing chamber and a cyclotron frequency fc is fc>fe.
In the above-mentioned plasma processing apparatus, the magnetic
field forming unit forms a magnetic field including a perpendicular
magnetic field at the specific plasma generating location. Further,
the magnetic field forming unit is provided on an outer peripheral
portion or a lateral portion of an antenna unit provided at a
ceiling of the processing chamber.
In the above-mentioned plasma processing apparatus, the specific
plasma generating location is provided at a location of 50% or more
spaced from a center location of the processing chamber with
respect to a diameter of the processing chamber in the antenna unit
provided in the ceiling of the processing chamber. Further, the
specific plasma generating location is formed outside the
peripheral portion of an object to be processed that is placed in
the processing chamber. Furthermore, the specific plasma generating
location is at least one of a location of a slot hole formed in the
antenna unit and a location along a concave portion.
In the above-mentioned plasma processing apparatus, a gap between
the ceiling of the processing chamber and the placed object to be
processed is set such that the magnetic field formed by the
magnetic field forming unit does not reach the placed object to be
processed.
In the above-mentioned plasma processing apparatus, the control
unit controls a pressure in the processing chamber to be 50 mTorr
(6.66 Pa) or less.
Further, a plasma processing apparatus according to another
exemplary embodiment of the present disclosure includes: a
processing chamber into which gas is introduced to generate plasma;
a magnetic field forming unit provided outside the processing
chamber and configured to form a magnetic field in a direction
perpendicular to an object to be processed that is placed in the
processing chamber; an oscillator configured to output
high-frequency power; an antenna unit provided in the processing
chamber and configured to supply the high-frequency power output by
the oscillator to the processing chamber; and a control unit
configured to control the magnetic field formed by the magnetic
field forming unit such that a relationship between an electron
collision frequency fe of plasma generated in the processing
chamber and a cyclotron frequency fc is fc>fe.
In the above-mentioned plasma processing apparatus, the antenna
unit has a plurality of slot holes and introduces a microwave
propagated into a waveguide through the plurality of slot holes
into the processing chamber, and the plurality of slot holes is
placed at a location of 50% or more spaced from a center location
of the processing chamber with respect to a radius of the
processing chamber. Further, the plurality of slot holes is placed
outside the peripheral portion of the placed object to be
processed.
In the above-mentioned plasma processing apparatus, the control
unit controls the intensity of the magnetic field formed by the
magnetic field forming unit to be 1 G to 50 G (10.sup.-4 T to
50.sup.-3 T).
In the above-mentioned plasma processing apparatus, the gas
introduced into the processing chamber is argon gas, and the
control unit controls an electron temperature of plasma generated
in the processing chamber to be 0.5 eV to 5 eV.
In the above-mentioned plasma processing apparatus, the control
unit controls a pressure in the processing chamber to be 20 mT to
200 mT (2.67 Pa to 26.7 Pa). Further, the control unit switches ON
and OFF of application of the magnetic field in time division, and
pulse-controls the magnetic field.
Further, a plasma processing method according to yet another
exemplary embodiment of the present disclosure includes: supplying
high-frequency power from a specific plasma generating location
into a processing chamber; forming a magnetic field at least at the
specific plasma generating location, which is provided outside the
processing chamber; and controlling the magnetic field such that a
relationship between an electron collision frequency fe of plasma
generated in the processing chamber and a cyclotron frequency fc is
fc>fe.
In the above-mentioned plasma processing method, the controlling of
the magnetic field includes switching ON and OFF of application of
the magnetic field in time division and pulse-controlling the
magnetic field.
In the above-mentioned plasma processing method, the specific
plasma generating location is around just below a transmission
plate serving as a dielectric window passing the high-frequency
power and electron density of plasma just below the transmission
plate is higher than frequency cutoff density of the high-frequency
power.
According to exemplary embodiments of the present disclosure,
controllability of a plasma distribution may be improved by
appropriating an applied magnetic field.
Hereinafter, exemplary embodiments of the present disclosure will
be described with reference to the accompanying drawings. Further,
in the specification and drawings, like reference numerals refer to
substantially like elements, and as a result, a duplicated
description will be omitted.
First Exemplary Embodiment
Overall Configuration of Radial Line Slot Antenna Apparatus
First, an overall configuration of a radial line slot antenna
apparatus according to a first exemplary embodiment of the present
disclosure will be described with reference to FIG. 1. FIG. 1 is a
longitudinal cross-sectional view of a radial line slot antenna
apparatus according to the first exemplary embodiment of the
present disclosure. In a radial line slot antenna apparatus 100, a
microwave is introduced into a processing chamber through a plane
type antenna having a plurality of slots, for example, a radial
line slot antenna. In the radial line slot antenna apparatus 100,
plasma excited by the microwave is surface wave plasma (SWP)
excited by a surface wave propagated on an interface of a
dielectric just below the antenna and plasma. The surface wave
plasma has high electron density of plasma throughout a wide area
just below the antenna. As a result, it is possible to perform
uniform plasma processing within a short time. Further, since the
surface wave plasma is at a low electron temperature, damage to an
element may be decreased.
The radial line slot antenna apparatus 100 has a substantially
cylindrical grounded chamber (processing chamber) 1. A wafer W is
carried into the chamber 1 in an airtight state. The chamber 1
includes a housing 2 and a cylindrical chamber wall 3 placed
thereabove. The housing 2 and the chamber wall 3 are made of a
metallic material such as aluminum or stainless steel. Further, a
microwave introduction unit 30 for introducing the microwave into a
processing space is provided above the chamber 1 to be openable and
closable.
An exhaust chamber 11 is provided below the housing 2 to
communicate with an opening portion 10 formed at the center of a
bottom plate of the housing 2. An inner part of the chamber 1 is
evenly exhausted by the exhaust chamber 11.
A susceptor 5 that horizontally supports the wafer W which is a
target of the plasma processing is provided in the housing 2. In
detail, the susceptor 5 is supported by a cylindrical support
member 4 that is extended upwardly from the center of a bottom of
the exhaust chamber 11. The susceptor 5 and the support member 4
may be made of a ceramic material such as quartz or AlN or
Al.sub.2O.sub.3. In particular, the susceptor 5 and the support
member 4 may be made of AlN having high thermal conductivity. A
guide ring 8 for guiding the wafer W is provided at an outer edge
of the susceptor 5. Further, a resistance heating type heater 6a is
buried in the susceptor 5, the susceptor 5 is heated by feeding
power from a heater power supply 6, and the wafer W supported by
the susceptor 5 is heated by the heat. The temperature of the
susceptor 5 is measured by a thermocouple 20 inserted into the
susceptor 5. A control unit 21 controls current supplied to the
heater from the heater power supply 6 based on a measurement value.
For example, the temperature of the heater 6a is adjusted to a
range of a room temperature to 1,000.degree. C.
Further, a wafer support pin (not illustrated) for supporting and
elevating the wafer W is provided in the susceptor 5. The wafer
support pin may protrude upwardly of the susceptor 5 and retreat
downwardly of the susceptor 5. A baffle plate 7 for evenly
exhausting the inside of the chamber 1 is circularly provided
outside the susceptor 5. The baffle plate 7 is supported by a
plurality of pillars 7a. A cylindrical liner 42 made of quartz is
provided on an inner periphery of the chamber 1. The liner 42
serves to prevent metal contamination from the chamber 1 made of
the metallic material. The liner 42 may be made of ceramics
(Al.sub.2O.sub.3, AlN, Y.sub.2O.sub.3, or the like) instead of
quartz.
An exhaust pipe 23 is connected to the lateral side of the exhaust
chamber 11. An exhaust device 24 including a high-speed vacuum pump
is connected to the exhaust pipe 23. Gas in the chamber 1 is evenly
discharged into a space 11a of the exhaust chamber 11 by actuating
the exhaust device 24 and then exhausted through the exhaust pipe
23. Therefore, pressure in the chamber 1 may be rapidly dropped to
approximately a predetermined degree of vacuum, for example, 2.67
Pa.
Carry-in and out ports for carrying the wafer W in and out the
wafer W, and a gate valve opening and closing the carry-in and out
ports are provided on a side wall of the housing 2 (all not
illustrated). A gas introduction path for introducing processing
gas into the chamber 1 is formed in the chamber 1. In detail, a
circular passage 13 is formed by a step portion 18 formed on the
top of the side wall of the housing 2 and a step portion 19 formed
on the bottom of the chamber wall 3 to be described below.
The top of the chamber wall 3 engages with the microwave
introduction unit 30 with a seal member 9c such as, for example, an
O-ring. The bottom of the chamber wall 3 is joined with the top of
the housing 2 with seal members 9a and 9b such as, for example, an
O-ring. An airtight state is maintained between the chamber wall 3
and the microwave introduction unit 30 and between the chamber wall
3 and the housing 2 by the seal members. Further, a gas passage 14
is formed in the chamber wall 3.
A circular protrusion portion 17 that is extended downwardly in a
skirt shape is formed on the bottom of the chamber wall 3. The
protrusion portion 17 covers a boundary (an interface portion)
between the chamber wall 3 and the housing 2 to prevent the seal
member 9b having comparatively low plasma resistance from being
directly exposed to plasma. Further, the step portion 19 is
provided on the bottom of the chamber wall 3 so as to form the
circular passage 13 through combination with the step portion 18 of
the housing 2.
Further, a plurality of (for example, 32) gas introduction ports
15a is evenly provided on an inner periphery above the chamber wall
3. The gas introduction port 15a communicates with the gas passage
14 that is extended in a vertical direction in the chamber wall 3
through an introduction path 15b that is horizontally extended into
the chamber wall 3.
The gas passage 14 is connected to a circular passage 13, which is
configured by a groove formed by the step portion 18 and the step
portion 19, at an interface portion between an upper portion of the
housing 2 and a lower portion of the chamber wall 3. The circular
passage 13 is circularly formed substantially in a horizontal
direction to surround the processing space. Further, the circular
passage 13 is connected with a passage 12, which is formed to be
extended vertically in the side wall of the housing 2, at
predetermined points (for example, four uniform points) in the
housing 2, and the passage 12 is connected with a gas supply device
16. The circular passage 13 serves as a gas distributing unit that
evenly supplies gas to each gas passage 14. A large amount of
processing gas is prevented from being supplied to the processing
space from a specific gas introduction port 15a by the circular
passage 13.
As described above, in the present exemplary embodiment, since gas
from the gas supply device 16 may be uniformly introduced from 32
gas introduction ports 15a through the passage 12, the circular
passage 13 and each of the gas passages 14 into the chamber 1,
uniformity of plasma in the chamber 1 may be increased.
As described above, since the chamber 1 is constituted by the
housing 2 and the cylindrical chamber wall 3 placed thereabove, the
chamber 1 is opened upwardly. The opening is air-tightly closed by
the microwave introduction unit 30. However, the microwave
introduction unit 30 is openable and closable by an opening and
closing mechanism (not illustrated).
The microwave introduction unit 30 includes a transmission plate
28, an antenna 31 placed above the transmission plate 28, and a
slow-wave member 33 placed on the top of the antenna 31. They are
covered with a shield member 34. Further, the transmission plate
28, the antenna 31, and the slow-wave member 33 are fixed to a
support member of an upper plate 27 via the O-ring by a circular
press sing 35 having an L shape when viewed from a cross section
through a support member 36. When the microwave introduction unit
30 is closed, the top of the chamber 1 and the upper plate 27 are
sealed by the seal member 9c. Further, the antenna 31 and the
slow-wave member 33 are supported on the upper plate 27 through the
transmission plate 28.
The transmission plate 28 is made of ceramics such as a dielectric,
in detail, quartz or Al.sub.2O.sub.3, AlN, sapphire, SiN, or the
like. The transmission plate 28 serves as a microwave introduction
window (dielectric window) that transmits the microwave and
introduces the microwave into the processing space in the chamber
1. A bottom surface (opposite surface of the susceptor 5) of the
transmission plate 28 is not limited to a flat type and for
example, a concave portion or a groove may be formed in order to
stabilize plasma by uniformizing the microwave. Since difference
pressure between atmospheric pressure and internal pressure of a
processing container is applied to the transmission plate 28, the
thickness of the transmission plate 28 of the plate type needs to
be 20 mm to 30 mm, but the thickness of the transmission plate 28
having a dome shape may be reduced by approximately 10% to 20%.
The bottom surface of the transmission plate 28 is supported on an
outer peripheral thereof via the seal member 29, by a circular
protrusion portion 27a that is radially extended inwardly from the
upper plate 27. When the microwave introduction unit 30 is closed
by the circular protrusion portion 27a, the inner part of the
chamber 1 may be air-tightly maintained.
The antenna 31 has a disk shape. Further, the antenna 31 is
suspended on an inner peripheral surface of the shield member 34
above the transmission plate 28. The surface of the antenna 31 is
configured by, for example, a copper plate or an aluminum plate
plated with gold or silver. A slot hole 32a (hereinafter, also
referred to as slot 1) on an inner peripheral side and a slot hole
32b (hereinafter, also referred to as slot 2) on an outer
peripheral side that penetrate the antenna 31 are formed in the
antenna 31 in a predetermined pattern. The slot holes 32a, 32b
radiate an electronic wave such as the microwave.
As illustrated in FIG. 2, in the first exemplary embodiment, the
slot holes 32a, 32b formed in the antenna 31 form a `T` shape by
combining two adjacent slot holes. The plurality of slot holes 32a,
32b is placed in a concentric shape as illustrated in FIG. 2.
Further, the shapes of the slot holes 32a, 32b are not limited
thereto, and may be a ring shape, an arc shape, or a spiral
shape.
The slow-wave member 33 is provided on a top surface of the antenna
31. The slow-wave member 33 has permittivity higher than vacuum
permittivity and is made of, for example, quartz, ceramics, a
fluorine resin such as polytetrafluoroethylene, or a polyimide
resin. A wavelength of the microwave in the slow-wave member 32 is
shorter than a wavelength of a microwave in vacuum. That is, the
slow-wave member 32 serves to adjust an electric wave of plasma.
Further, the transmission plate 28 and the antenna 31 may be
closely attached to or separated from each other. In addition, the
antenna 31 and the slow-wave member 33 may be closely attached to
or separated from each other.
A cooling water path (not illustrated) is formed in the shield
member 34, and it is possible to cool the shield member 34, the
slow-wave member 33, the antenna 31, the transmission plate 28, and
the upper plate 27 by flowing cooling water on the cooling water
path. Therefore, deformation or breakage of the members is
prevented to generate stable plasma. Further, the shield member 34
is grounded.
A waveguide 37 is connected to an opening of the center of the
shield member 34. A microwave generating device 39 is connected to
an end of the waveguide 37 through a matching circuit 38.
Therefore, a microwave having, for example, a frequency of 2.45
GHz, which is generated by the microwave generating device 39, is
propagated to the antenna 31 through the waveguide 37. The
frequency of the microwave may be 8.35 GHz, 1.98 GHz, or the
like.
The waveguide 37 includes a coaxial waveguide 37a having a circular
cross section, which is extended upwardly from the opening portion
of the shield member 34, and a rectangular waveguide 37b connected
to the top of the coaxial waveguide 37a through a mode converter
40. The mode converter 40 between the rectangular waveguide 37b and
the coaxial waveguide 37a serves to convert a microwave propagated
in a TE mode into a microwave in a TEM mode in the rectangular
waveguide 37b. An internal conductor 41 is extended at the center
of the coaxial waveguide 37a and the internal conductor 41 is
connected and fixed to the center of the antenna 31 on the bottom
thereof. Therefore, the microwave is efficiently and evenly
propagated to the antenna 31 in a radial pattern.
A coil 52 for generating a magnetic field is wound in a radius
direction of the chamber 1 around the side wall of the chamber 1,
outside the chamber 1. When a power supply 53 is connected to the
coil 52 and current from the power supply 53 flows on the coil 52,
a perpendicular-direction (vertical-direction) magnetic field
(hereinafter, referred to as a vertical magnetic field) to the
chamber 1 is formed in the chamber 1. The size and a vertical
direction of the magnetic field may be changed by changing a
current value from the power supply 53. In the first embodiment, a
horizontal-direction (transverse-direction) magnetic field
(hereinafter, simply referred to as a transverse magnetic field) to
the chamber 1 is not required.
Further, a permanent magnet may be provided instead of the coil 52.
In this case, a plurality of pole type permanent magnets vertically
polarized into N and S poles may be erected around the side wall of
the chamber 1 or a permanent magnet having an N pole at any one
side and an S pole at the other side among a ceiling and a bottom
of the chamber 1 may be placed outside the chamber 1. As a result,
the vertical magnetic field may be formed in the chamber 1.
A control unit 70 has a central processing unit (CPU), a read only
memory (ROM) and a random access memory (RAM), which are not
illustrated, and the CPU executes plasma processing according to
various recipes stored in the storage areas. A process time, the
temperature (the temperature of an upper electrode, the temperature
of a side wall of the processing chamber, an ESC temperature, and
the like) in the processing chamber, pressure (exhaust of gas),
various process gas flow rates, and the like which are control
information for the process condition are disclosed in the recipe.
For example, the control unit 70 controls an output of the power
supply 53 in order to control the vertical magnetic field formed in
the chamber 1. Further, a function of the control unit 70 may be
implemented by operating the control unit 70 by using software or
implemented by operating the control unit 70 by using hardware.
As described above, the overall configuration of the radial line
slot antenna apparatus 100 according to the embodiment has been
described. In the radial line slot antenna apparatus 100 having the
above configuration, when the microwave is introduced into the
chamber 1, gas is excited by field energy of the introduced
microwave and microwave plasma is generated. In the radial line
slot antenna apparatus 100, when a specific plasma generating
location is approximately just below the transmission plate 28
serving as the dielectric window that allows high-frequency power
to pass, and when electron density of plasma just below the
transmission plate is higher than frequency cutoff density of the
high-frequency power, the microwave may not enter plasma and is
propagated between the bottom surface of the transmission plate 28
and plasma, and some of the microwave is absorbed in plasma to used
to hold plasma.
According to such a generation principle of plasma, the microwave
plasma is high in electron density Ne and low in electron
temperature Te of plasma as compared with capacitively coupled
plasma (CCP), inductively coupled plasma (ICP), and electron
cyclotron resonance plasma (EC), and therefore a high-quality
product may be manufactured by plasma processing which is at high
speed and is a little in damage.
[Electron Density of Plasma]
(Control by Slot Location)
As illustrated in FIG. 3, the microwave is propagated in the
waveguide 37 (coaxial waveguide 37a), passes through the plurality
of slot holes 32a, 32b from the slow-wave member 33, and transmits
the transmission plate 28, and is thus introduced into the chamber
1. The microwave becomes a standing wave in the transmission plate
28. The standing wave forms a field intensity distribution in which
lower portions of the slot holes 32a, 32b have maximum field
intensity. Therefore, a distribution is formed, in which electron
density of plasma formed in a plasma space U is highest at the
lower portions of the slot holes 32a, 32b.
In the embodiment, the slot hole 32b is formed at a location
radially spaced by 16 cm from a center location of the chamber 1,
and the slot hole 32a is formed at a location radially spaced by 9
cm from the center location of the chamber 1. In the present
exemplary embodiment, a diameter of the wafer W is 300 mm and in
other words, the location of the slot hole 32b is positioned
outside an outer edge of the wafer W. However, each slot location
is not limited thereto. The slot hole 32b may be placed at a
location of 50% or more spaced from the center location of the
chamber 1 with respect to a radius of the chamber 1 and the slot
hole 32a may be placed at a location of 50% or less from the center
location of the chamber 1 with respect to the radius of the chamber
1.
When the antenna 31 has only the slot hole 32b, a peak of the
electron density of generated plasma is at the lower portion of the
slot hole 32b, that is, at the location of 50% or more spaced from
the center location of the chamber 1. When the antenna 31 has only
the slot hole 32a, a peak of the electron density of generated
plasma is at the lower portion of the slot hole 32a, that is, at
the location of 50% or less from the center location of the chamber
1. Therefore, the peak of the electron density of plasma when the
slot hole 32b is formed is present on an outer peripheral side than
the peak of the electron density of plasma when the slot hole 32a
is formed. By this configuration, an electron density distribution
of plasma may be controlled at locations where one or more slot
holes are formed.
(Control by Magnetic Field)
Further, the electron density distribution of plasma may be
controlled even by the vertical magnetic field. For example, FIG. 4
is a diagram illustrating a simulation result of the electron
density distribution of plasma in a radius direction from the
center of the chamber 1 by a contour line. FIG. 4A illustrates a
case where the vertical magnetic field is not applied and FIG. 4B
illustrates a case where the vertical magnetic field is
applied.
As a precondition for executing a simulation, in the case of a
process condition, a gas type was set as argon gas (Ar), a pressure
in the chamber 1 was set to 20 mT (2.67 Pa), and the size of the
vertical magnetic field was set to 10 G (10.sup.-3 T).
As a result, the electron density Ne of plasma when the case where
the magnetic field is not applied, which is illustrated in FIG. 4A,
has a distribution in which the electron density Ne is higher at
the center side than at the outer peripheral side of the chamber 1.
As a result, an etching rate is also higher at the center side than
at the outer peripheral side to cause uniformity of a process such
as, for example, plasma etching to be short.
In particular, under a low-pressure condition of 50 mTorr (6.66 Pa)
or less, the electron density Ne of plasma has a pronounced
tendency to be higher at the center side and lower at the outer
peripheral side, and thus, for example, the uniformity of plasma
etching deteriorates. In particular, the reason why the electron
density Ne of plasma is higher at the center side under the
low-pressure condition is that it is difficult for electrons or
ions in plasma to collide with each other and plasma is easily
diffused in a low-pressure state. As a result, areas where the
electron density Ne of plasma is high are concentrated on the
center side, such that it is more difficult to control plasma.
Contrary to this, in the case of the electron density Ne of plasma
when a vertical magnetic field B is applied, which is illustrated
in FIG. 4B, areas where the electron density Ne of plasma is high
move from the center side to the outer peripheral side. From the
above result, it is seen that the vertical magnetic field B is
applied to change the electron density distribution of plasma.
As such, the area where the electron density Ne of plasma is high
moves from the center side to the outer peripheral side by the
location of the slot and the application of the vertical magnetic
field, thereby improving controllability of a plasma distribution.
Herein, high controllability of the plasma distribution unit that
the process condition is optimized to uniformize plasma. When the
areas where the electron density Ne of plasma is high concentrate
on the center side, it is difficult to optimize the process
condition for uniformizing plasma. Contrary to this, when the area
where the electron density Ne of plasma is high is positioned at
the outer peripheral side (an area of at least 50% or more of the
radius of the chamber 1), it is easy to optimize the process
condition for uniformizing plasma.
As described above, while the slot is positioned at the location of
at least 50% or more of the radius of the chamber 1 from the center
side of the chamber 1, the vertical magnetic field B of
approximately 10 G (10.sup.-3 T) or more may be primarily applied
to the chamber 1. In this case, a gap length between the wafer W
and the transmission plate 28 may be equal to or less than the
radius of the chamber 1.
Further, the process condition needs to be set such that at least a
cyclotron frequency is higher than a collision frequency of
electrons. Hereinafter, a relationship between the cyclotron
frequency and the collision frequency of the electrons will be
described.
[Cyclotron Frequency and Electron Collision Frequency of
Plasma]
FIG. 5 is a graph illustrating a relationship between an electron
collision frequency fe of plasma generated from argon (Ar) gas and
a cyclotron frequency fc. In FIG. 5, a transverse axis indicates an
electron temperature of plasma and a longitudinal axis indicates a
collision frequency. A result of FIG. 5 may be obtained by a
simulation based on a simulation condition and a process condition
described below.
<Simulation Condition>
In a simulation performed in the embodiment, a plasma calculation
method using a 2D bipolar diffusion approximation (2D quasi neutral
plasma model) is used. For example, as the plasma calculation
method using the 2D bipolar diffusion approximation, methods
disclosed in Documents 1 and 2 below may be used. Document 1: A.
Tsuji, Y. Yasaka, S. Y. Kang, T. Morimoto, I. Sawada, Thin Solid
Films 516, 4368, 2008 Document 2: J. Brcka and S. Y. Kang, Plasma
Process. Polym. 6, S776, 2009
<Process Condition>
Pressure in chamber 1: 20 mT (2.67 Pa), 200 mT (26.7 Pa), 2T (267
Pa)
Microwave power: 3 kW
Gas type/gas flow rate: Argon gas (Ar) 1,000 sccm
Vertical magnetic field: 1 G to 50 G (10.sup.-4 T to 50.sup.-3
T)
The electron collision frequency fe of plasma may be expressed by a
frequency at which electrons collide with particles (in this case,
argon particles) in the chamber 1. In the simulation, the electron
collision frequency fe of plasma is approximately acquired by
multiplying a reaction rate constant of argon gas (a reaction rate
constant in elastic collision of electrons and neutral particles
(in this case, argon particles)) by the density of gas. The
reaction rate constant of argon gas is acquired by using Equation 1
below.
.times..times..function..times..function..function..times..times.
##EQU00001##
Herein, T.sub.e[k] in Equation 1 represents an electron temperature
of plasma.
Based on the result of the simulation, the electron collision
frequencies fe of argon plasma at 20 mT, 200 mT, and 2 T and the
cyclotron frequencies fc of three patterns at 1 G (10.sup.-4 T), 5
G (50.sup.-4 T), and 50 G (50.sup.-3 T) are illustrated in FIG.
5.
According to the simulation result of FIG. 5, it can be seen that
the electron collision frequency fe of plasma is changed depending
on a pressure and the electron temperature of plasma. In detail, as
the pressure increases, the electron collision frequency fc of
plasma increases. The reason is that as the pressure increases, the
number of electrons present in a plasma space increases such that
the collision frequency of the electrons increases.
Further, as the electron temperature of plasma increases, the
electron collision frequency fe of plasma increases. The reason is
that as the electron temperature of plasma increases, a movement
speed of the electron increases such that the electron collision
frequency increases. Further, the electron collision frequency fe
of plasma is changed even depending on the gas type.
Meanwhile, it can be seen that the cyclotron frequency fc of FIG. 5
is changed depending on the size of the applied vertical magnetic
field. In detail, as the vertical magnetic field increases, the
cyclotron frequency fc increases. However, the cyclotron frequency
fc is not changed depending on the level of the electron
temperature of plasma. The cyclotron frequency fc is acquired by
using Equation 2 below.
.function..times..function..function..times..times..pi..times..times.
##EQU00002##
Herein, q represents an elementary charge, m.sub.e represents a
mass of the electron, and B represents the magnetic field.
A condition needs to be met, which `the cyclotron frequency fc when
the vertical magnetic field is applied is higher than the electron
collision frequency fe of plasma`, in order for the application of
the vertical magnetic field and the application of the magnetic
field including the vertical magnetic field and the transverse
magnetic field to influence the controllability of the plasma
distribution. The reason will be described below. By considering
movement of electrons in plasma, when the electron collision
frequency fe is higher than the cyclotron frequency fc, a frequency
at which the electrons collide with particles in the chamber 1 is
relatively high, and as a result, even though the vertical magnetic
field is applied, a probability that the electrons move due to the
vertical magnetic field is relatively low. That is, when the
electron collision frequency fe is higher than the cyclotron
frequency fc, the electrons predominately collide with the
particles in the chamber 1, and as a result, it is difficult to
control the electrons by the vertical magnetic field. Therefore,
when the electron collision frequency fe is higher than the
cyclotron frequency fc, it is difficult to shift the area where the
electron density of plasma is high from the center side to the
outer peripheral side.
Meanwhile, when the cyclotron frequency fc is higher than the
electron collision frequency fe, the frequency at which the
electrons collide with the particles in the chamber 11 is
relatively decreased, and as a result, a probability that the
electrons move due to the applied vertical magnetic field is
relatively increased. That is, when the cyclotron frequency fc is
higher than the electron collision frequency fe, the electrons
predominately move due to the vertical magnetic field, and as a
result, it is possible to control the electrons by the vertical
magnetic field. Therefore, when the cyclotron frequency fc is
higher than the electron collision frequency fe, it is possible to
shift the area where the electron density of plasma is high from
the center to the outer peripheral side. Therefore, it is possible
to improve the controllability of the plasma distribution.
Actually, in order to meet a condition that the cyclotron frequency
fc is higher than the electron collision frequency fe, the vertical
magnetic field, the pressure, the electron temperature of plasma,
and the like need to be optimized. For example, it is possible to
meet the condition that the cyclotron frequency fc is higher than
the electron collision frequency fe, by the vertical magnetic field
controlled by the control unit 70.
As described above, when the magnetic field is not applied, the
controllability of the plasma distribution tends to deteriorate as
the pressure becomes lower. However, according to the simulation
result of FIG. 5, a larger vertical magnetic field needs to be
applied as the pressure becomes higher, in order to meet the
condition that the cyclotron frequency fc is higher than the
electron collision frequency fe of plasma. Contrary to this, the
condition may be met even in a smaller vertical magnetic field as
the pressure becomes lower. Therefore, in the plasma control using
the vertical magnetic field according to the embodiment, one of the
features is that it is possible to effectively control plasma as
the pressure becomes lower.
Further, according to the simulation result of FIG. 5, the
condition that the cyclotron frequency fc is higher than the
electron collision frequency fe of plasma is met in an area at a
low electron temperature. Therefore, in the embodiment, one of the
features is that it is possible to effectively control the plasma
distribution in an area at a lower electron temperature. The radial
line slot antenna apparatus 100 that performs plasma processing
according to the embodiment has one of the features, even that the
plasma control and compatibility of the embodiment are also
excellent because plasma at the low electron temperature may be
generated.
As described above, by the plasma control according to the
embodiment, it is possible to edge-shift the area where the
electron density of plasma is high from the center side to the
outer peripheral side, in particular, at a low-pressure state
without greatly influencing ion flux by using a vertical magnetic
field having a predetermined degree of intensity, by optimization
of the location of the slot or the applied vertical magnetic field.
Therefore, it is possible to improve the controllability of the
plasma distribution.
Herein, the vertical magnetic field having a predetermined degree
of intensity represents a vertical magnetic field of approximately
1 G to 50 G (10.sup.-4 T to 50.sup.-3 T). When an influence by the
magnetic field on the wafer W during the process is considered, it
is not preferable to apply a vertical magnetic field having a
larger intensity during the process. The plasma control according
to the embodiment is excellent even in that the plasma control by
the small vertical magnetic field of approximately 1 G to 50 G
(10.sup.-4 T to 50.sup.-3 T) may be executed without influencing
the process.
However, when the vertical magnetic field in the range of 1 G to 50
G (10.sup.-4 T to 50.sup.-3 T) is applied, a pressure band, which
meets the condition that the cyclotron frequency fc is higher than
the electron collision frequency fe of plasma, is changed depending
on the gas type and the electron temperature of plasma. In the
plasma generated from the argon gas of FIG. 5, in order to meet the
condition that the cyclotron frequency fc is higher than the
electron collision frequency fe of plasma, the electron temperature
of plasma is preferably in the range of 0.5 eV to 5 eV and the
pressure in the chamber is controlled to be 20 mT to 200 mT (2.67
Pa to 26.7 Pa).
[Optimization of Slot Location and Magnetic Field]
Next, a simulation result, which is performed for achieving
optimizeness of the slot location [slot 1 and slot 2] and
optimizeness of the magnetic field (vertical magnetic field and
transverse magnetic field), will be described. In the simulation,
the plasma calculation method using the 2D bipolar diffusion
approximation is used. Slot 1 is the slot hole 32a illustrated in
FIG. 3 and a through-hole formed at the location of the 9 cm radius
from the center location of the chamber 1. Slot 2 is the slot hole
32ba illustrated in FIG. 3 and a through-hole formed at the
location of the 16 cm radius from the center location of the
chamber 1.
As a simulation condition of FIG. 6, in two cases of (a) a case
where the magnetic field is evenly applied in the radius direction
of the chamber; and (b) a case where a strong magnetic field is
applied toward the outer peripheral side from the center of the
chamber in the radius direction of the chamber (hereinafter, a case
where the magnetic field is slantly applied), a simulation result
when the vertical magnetic field is applied to the chamber is
calculated. The result is illustrated in FIG. 7.
In detail, FIG. 7A illustrates the electron density Ne of plasma in
the radius direction in a case where slot 1 (the slot hole 32a at
the center side of FIG. 3) is formed in the antenna 31 as a case
where the vertical magnetic field is evenly applied as illustrated
in FIG. 6A.
FIG. 7B illustrates the electron density Ne of plasma in the radius
direction in a case where slot 2 (the slot hole 32b at the outer
peripheral side of FIG. 3) is formed in the antenna 31 as the case
where the vertical magnetic field is evenly applied as illustrated
in FIG. 6A.
FIG. 7C illustrates the electron density Ne of plasma in the radius
direction in the case where slot 1 (the slot hole 32a at the center
side of FIG. 3) is formed in the antenna 31 as a case where the
vertical magnetic field is slantly applied as illustrated in FIG.
6B.
FIG. 7D illustrates the electron density Ne of plasma in the radius
direction in the case where slot 2 (the slot hole 32b at the outer
peripheral side of FIG. 3) is formed in the antenna 31 as the case
where the vertical magnetic field is slantly applied as illustrated
in FIG. 6B.
As a result, referring to FIGS. 7A to 7D, when the vertical
magnetic field is applied [1 G (10.sup.-4 T), 5 G (50.sup.-4 T), 10
G (10.sup.-3 T), 50 G (50.sup.-3 T)], it can be seen that the peak
of the electron density Ne of plasma may be moved from the center
side to the outer peripheral side, as compared with the case where
the magnetic field is not applied (B=0). In this case, when the
vertical magnetic field is applied (1 G, 5 G, 10 G, and 50 G), the
controllability of the plasma distribution by the magnetic field
becomes higher as a variation width of the electron density
distribution of plasma becomes larger, as compared with the case
where the magnetic field is not applied (B=0).
From this point of view, when FIGS. 7A to 7D are considered, it can
be seen that the controllability of the plasma distribution is
higher at the location of slot 2 illustrated in FIGS. 7B and 7D
than at the location of slot 1 illustrated in FIGS. 7A and 7C.
Further, it can be seen that the controllability of the plasma
distribution is higher in `the case where the vertical magnetic
field is evenly applied` of FIGS. 7A and 7B than in `the case where
the vertical magnetic field is slantly applied` of FIGS. 7C and
7D.
From the above, it can be seen that when the vertical magnetic
field is applied into the chamber, the following effects may be
obtained.
(1) When the vertical magnetic field is applied, the area where the
electron density Ne of plasma is high may be moved from the center
side to the outer peripheral side, thereby improving the
controllability of the plasma distribution, as compared with the
case where the magnetic field is not applied (B=0).
(2) When slot 2 at the outer peripheral side is formed, the
influence on the electron density Ne of plasma by the vertical
magnetic field may become larger and the area where the electron
density Ne of plasma is high may be moved more largely from the
center side to the outer peripheral side, thereby further improving
the controllability of the plasma distribution, as compared with
the case where slot 1 at the center side is formed.
(3) When the magnetic field is evenly applied, the peak of the
electron density Ne of plasma may be moved more largely from the
center side to the outer peripheral side, thereby further improving
the controllability of the plasma distribution, as compared with
the case where the magnetic field is not evenly applied.
Therefore, it can be seen that when the slot is formed at the outer
peripheral side (the location of 50% or more spaced from the center
location of the chamber) like slot 2, and the even vertical
magnetic field is applied to the chamber, particularly the
controllability of the plasma distribution may be improved.
The result is digitized as controllability of plasma distribution
and illustrated in FIG. 8. The controllability of plasma
distribution is calculated by using the following Equation 3.
controllability=.intg..sub.0.sup.0.15[m]n.sub.erdr [Equation 3]
Here, in Equation 3, n.sub.e represents an electron density of the
plasma. A location r represents a radial location of the wafer from
a center of the wafer W to an outer edge of the wafer W (edge of
the wafer). That is, Equation 3 is a value obtained by integrating
the product of the electron density n.sub.e of the plasma and the
location r thereof from 0 mm to 150 mm in a radial direction of the
wafer.
In Equation 3, as the electron density n.sub.e of the plasma at the
outer peripheral side of the wafer W is increased, the
controllability of plasma distribution is increased.
Referring to FIG. 8, as described above, the highest
controllability is illustrated in `(a) slot 2` of FIG. 8. In this
case, the location of the slot is formed at the slot 2 of the outer
peripheral side, and a uniformly vertical magnetic field is
applied. The second highest controllability is the location of the
slot is formed at the slot 2 of the outer peripheral side, and the
vertical magnetic field is slantly applied, as illustrated in `(b)
slot 2` of FIG. 8.
The third highest controllability is the location of the slot is
formed at the slot 1 of an inner peripheral side, and a uniform
magnetic field is applied, as illustrated in `(a) slot 1` of FIG.
8. The lowest controllability is the location of the slot is formed
at the slot 1 of the inner peripheral side, and the vertical
magnetic field is slantly applied, as illustrated in `(b) slot 1`
of FIG. 8. Hereinabove, an influence which the slot location and
the vertical magnetic field give to the controllability of plasma
distribution is verified.
Next, when the applied magnetic field is a transverse magnetic
field, an influence which the slot location and the horizontal
magnetic field give to the controllability of plasma distribution
will be verified. In detail, FIG. 9A illustrates an electron
density Ne of plasma of a radial direction in the case where the
slot 1 (the slot hole 32a at the center side of FIG. 3) is formed
in the antenna 31, as a case where the horizontal magnetic field is
uniformly applied as illustrated in FIG. 6A.
FIG. 9B illustrates an electron density Ne of plasma of a radial
direction in the case where the slot 2 (the slot hole 32b of the
outer peripheral side of FIG. 3) is formed in the antenna 31, as a
case where the horizontal magnetic field is uniformly applied as
illustrated in FIG. 6A.
According to FIGS. 9A and 9B, when the cases (1 G, 5 G, 10 G, and
50 G) where the horizontal magnetic field is applied are compared
with the case (B=0) where the horizontal magnetic field is not
applied, it is verified that the horizontal magnetic field does not
almost affect the distribution of the electron density Ne of
plasma. In detail, even though the horizontal magnetic field is
applied, a peak of the electron density Ne of plasma does not move
to the outside, and similarly to the case where the magnetic field
is not applied, the electron density Ne of plasma at the center is
high, and the electron density Ne of plasma at the outside is low.
That is, even though the horizontal magnetic field is applied,
since the electron density Ne of plasma is biased at the center, it
can be seen that there is no uniformity of the plasma, and the
controllability of plasma distribution is low.
From the above simulation result, it can be seen that the magnetic
field used for the control of the plasma in the embodiment needs to
be the vertical magnetic field applied in a vertical direction of
the chamber and there is no point to apply the horizontal magnetic
field.
According to Fleming's left-hand law, when the horizontal magnetic
field is applied such that force is applied to the outside, the
electrons move in a vertical direction, and the movement of the
electrons in a horizontal direction is constrained. That is, the
movement of the electrons in a radial direction of the chamber is
constrained. Accordingly, even though the horizontal magnetic field
is applied, the electron density of plasma is not shifted from the
center to the outside. As a result, even though the horizontal
magnetic field is applied, it is difficult to increase the
controllability of plasma distribution. Meanwhile, when the
vertical magnetic field is applied such that the force is applied
to the outside, the electrons move in a horizontal direction, and
the movement of the electrons in the vertical direction is
constrained. That is, the movement of the electrons in a radial
direction of the chamber is not constrained. Accordingly, when the
vertical magnetic field is applied, the electron density of plasma
is shifted from the center to the outside. As a result, when the
vertical magnetic field is applied, the controllability of plasma
distribution may be increased. Hereinabove, in the control of the
plasma according to the embodiment, it is necessary to apply the
vertical magnetic field.
[Pulse Control of Vertical Magnetic Field]
Finally, a simulation result in the case where a vertical magnetic
field is applied as a pulse type will be described. In the
simulation, a plasma calculation using 2D bipolar diffusion
approximation is used. When a slot is provided at a location of the
slot 2, and a magnetic field is turned on, a vertical magnetic
field of 10 G is applied.
The result is illustrated in FIG. 10. A transverse axis of FIG. 10
represents a distance in the radial direction of the wafer, and a
vertical axis thereof represents the electron density Ne of plasma.
A curve of `B on` represents the electron density Ne of plasma in
the case where the vertical magnetic field of 10 G is continuously
applied, and a curve of `B=0` represents the electron density Ne of
plasma in the case where the magnetic field is not applied. A curve
of `B pulse` represents the electron density Ne of plasma when
applying the vertical magnetic field of a pulse type, in which ON
and OFF of the vertical magnetic field are repeated by controlling
ON and OFF of the vertical magnetic field in time division.
The curve of `B pulse` is time average distribution of the curve of
`B on` and the curve of `B=0`, and an electron density distribution
Ne of plasma becomes more flat. That is, in the case where the
pulse type of vertical magnetic field is applied, the electron
density distribution of plasma having higher uniformity is acquired
as compared with the case where the vertical magnetic field is
continuously applied. Further, in the case where the pulse type of
vertical magnetic field is applied (the curve of `B pulse`), an
area having high electron density Ne of plasma may be further
shifted to the outside, thereby further improving the
controllability of plasma distribution. Meanwhile, the pulse
control of the vertical magnetic field is performed by the control
70. The control unit 70 switches ON and OFF of the application of
the vertical magnetic field in time division and pulse-controls the
vertical magnetic field.
Second Exemplary Embodiment
In a method in the related art, it was difficult to control the
plasma distribution under a low-pressure condition of 1 mTorr
(0.133 Pa) to 50 mTorr (6.66 Pa). As one scheme for controlling the
plasma distribution under the low-pressure condition, narrowing a
gap, which is a distance from the top surface of the wafer to the
bottom surface of the ceiling of the chamber 1, is considered.
However in this case, there is high possibility that damage to the
wafer will be caused during the process because the temperature of
the wafer is increased by irradiation of plasma. Further, since a
distribution of a standing wave unique to the surface wave plasma
influences processing of the wafer, such as, for example,
non-uniformity of the etching rate, the scheme is not a good
idea.
[Outline of Apparatus Configuration]
On the contrary, in a radial line slot antenna apparatus 100
according to a second embodiment, a relatively small magnetic field
of about 1 G (10.sup.-4 T) to 50 G (50.sup.-3 T) having two
components of a vertical magnetic field and a horizontal magnetic
field is applied. As a result, a method of controlling plasma
distribution even under the low-pressure condition of 1 mTorr to 50
mTorr is seen. Hereinafter, a configuration of the radial line slot
antenna apparatus 100 according to the second embodiment and a
control of the plasma distribution using the apparatus will be
described.
A basic configuration of the radial line slot antenna apparatus 100
according to the second embodiment is the same as the configuration
of the radial line slot antenna apparatus 100 according to the
first embodiment illustrated in FIG. 1.
The configuration of the radial line slot antenna apparatus 100
according to the second embodiment is different from the
configuration of the radial line slot antenna apparatus 100
according to the first embodiment in that the slot holes 32a and
32b formed in the first embodiment are not formed in the second
embodiment. In the second embodiment, instead, as illustrated in
FIG. 11, a concave portion 28b is formed at an outer peripheral
side of a bottom surface of the transmission plate 28 provided on a
ceiling of the radial line slot antenna apparatus 100.
An antenna unit 130 of the second embodiment includes the
transmission plate 28, and supplies a microwave propagated from a
surface of the internal conductor 41 into the chamber 1. Meanwhile,
the antenna unit of the first embodiment includes the antenna 31
and the transmission plate 28, and supplies the microwave
propagated from the surface of the internal conductor 41 into the
chamber 1. A power supply unit in each embodiment corresponds to
the antenna unit supplying high frequency power into the chamber 1
from a specific plasma generating location.
When passing through the transmission plate 28 from the center of
the antenna unit 130, the microwave is introduced into the chamber
1 through a propagation path defined by the formation of the
concave portion 28b. That is, the concave portion 28b is formed at
the outer peripheral side of the bottom surface of the transmission
plate 28, and as a result, the microwave passing through the
transmission plate 28 is output into the chamber 1 from the
internal center of the concave portion 28b and an end vicinity 28a
at the center of the concave portion 28b as the main propagation
paths. Accordingly, field intensities at the internal center of the
concave portion 28b and the end vicinity 28a at the center of the
concave portion 28b are higher than the field intensities at other
portions of the bottom surface of the transmission plate 28. As a
result, locations of the internal center of the concave portion 28b
and the end vicinity 28a at the center of the concave portion 28b
become a main power absorption location of the plasma. Hereinafter,
an inner plasma generating location 132a is disposed directly below
the location of the end vicinity 28a at the center of the concave
portion 28b, and an outer plasma generating location 132b is
disposed directly below the location of the internal center of the
concave portion 28b. A plasma generating region 1 (Region 1) is
formed below the inner plasma generating location 132a, and a
plasma generating region 2 (Region 2) is formed below the outer
plasma generating location 132b.
In the propagation path of the microwave and the output state
thereof in the chamber 1, which are described above, the slot hole
of the first embodiment and the concave portion of the second
embodiment have the same function.
The concave portion 28b is disposed at a location of 50% or more
spaced from the center location of the chamber 1 with respect to a
diameter of the chamber 1. In the embodiment, the specific plasma
generating location includes at least an outer plasma generating
location 132b. That is, the outer plasma generating location 132b
is an example of the specific plasma generating location, and may
be disposed at a location of 50% or more spaced from the center
location of the chamber 1 with respect to the diameter of the
chamber 1, and the inner plasma generating location 132a may be
disposed at any one location. In the embodiment, the inner plasma
generating location 132a is disposed at a location of 50% or less
from the center location of the chamber 1 with respect to a
diameter of the chamber 1. The specific plasma generating location
is not limited to the location of the outer plasma generating
location 132b in the embodiment, but one or two or more specific
plasma generating locations may be provided at a location of 50% or
more spaced from the center location of the chamber 1 with respect
to a diameter of the chamber 1. Further, the specific plasma
generating location may be formed further outside than a peripheral
edge of the wafer disposed in the chamber 1.
In the embodiment, an electromagnet 54 is provided in a ring shape
to surround the chamber 1 at a side wall of the antenna unit 130
outside the chamber 1. However, a layout or a shape of the
electromagnet 54 is not limited thereto, and the electromagnet 54
may be provided at any one location of the outer peripheral side of
the chamber 1 at the upper portion or the lateral portion of the
ceiling of the chamber 1. The outer peripheral side of the chamber
1 is a location of 50% or more spaced from the center location of
the chamber 1 with respect to a diameter of the chamber 1.
Particularly, the electromagnet 54 may be provided around an outer
end of the ceiling of the chamber 1. Further, the electromagnet 54
may be provided around the plasma generating location. As a result,
as illustrated in FIG. 12, a concentric circular magnetic field B
around the electromagnet 54 around the outer end of the ceiling of
the chamber 1 is generated. The electromagnetic 54 forms a magnetic
field including a vertical direction component and a component
outwards in a diameter direction of the chamber 1 inside the
chamber 1. Meanwhile, even though a magnetic field in a reverse
direction to the magnetic field illustrated in FIG. 12, that is, a
magnetic field in a clockwise direction is formed in addition to a
magnetic field in a counterclockwise direction illustrated in FIG.
12, it is possible to acquire an effect that the electrons move to
the outer peripheral side of the chamber 1. In this case, the
magnetic field in a reverse direction to the magnetic field
illustrated in FIG. 12 may be formed by running a current in a
reverse direction to the electromagnet 54 illustrated in FIG.
12.
The electromagnet 54 is provided outside the chamber 1 and an
example of a magnetic field forming unit of forming a magnetic
field including at least the vertical magnetic field at least at
the specific plasma generating location. The magnetic field forming
unit may be a permanent magnet. The coil 52 of the first embodiment
is an example of the magnetic field forming unit, but the magnetic
field formed by the magnetic field forming unit of the first
embodiment does not include a magnetic field (transverse magnetic
field) in a diameter direction of the chamber 1. Meanwhile, the
magnetic field formed by the magnetic field forming unit of the
second embodiment includes a vertical direction component and a
component outwards in the diameter direction.
Further, in the embodiment, a gap from the ceiling of the chamber 1
to the wafer W is set such that the magnetic field formed by the
electromagnet 54 does not reach the wafer W. In the embodiment, as
illustrated in FIG. 11, a gap from the upper surface of the wafer W
to the lower surface of the ceiling is 245 mm. The gap may be any
distance by which the electric field formed by the electromagnet 54
does not reach the wafer W.
Further, in the first embodiment, the relationship between the
electron collision frequency fe of plasma and the cyclotron
frequency fc is described with reference to FIG. 1, but even in the
second embodiment, the magnetic field is controlled such that the
relationship between the electron collision frequency fe of the
plasma formed in the chamber 1 and the cyclotron frequency fc
becomes fc>fe.
Hereinabove, the configuration of the radial line slot antenna
apparatus 100 according to the second embodiment has been
described.
[Magnetic Field]
(Plasma Control by Magnetic Field)
Next, in the radial line slot antenna apparatus 100 having the
aforementioned configuration, a simulation how a plasma state in
the plasma generating region is changed by presence of the
electromagnet 54 and a magnitude of a magnetic flux density is
performed. FIG. 13 illustrates a contour line of the magnetic field
used in the simulation. In the simulation, a case where three kinds
of magnetic fields of a magnetic field of 2 G to 8 G
(2.times.10.sup.-4 T to 8.times.10.sup.-4 T), a magnetic field of
3.8 G to 17 G (3.8.times.10.sup.-4 T to 1.7.times.10.sup.-3 T), and
a magnetic field of 7 G to 33 G (7.times.10.sup.-4 T to
3.3.times.10.sup.-3 T) are formed as relatively small magnetic
fields and a case where the magnetic field is not formed are set as
a condition of the simulation for the magnetic field.
As a result of the simulation, the electron density Ne of plasma
and an electron temperature Te are illustrated in FIG. 14 as the
contour line. The electron density Ne (1/m.sup.3) of plasma formed
below the ceiling surface and the electron temperature Te (eV) are
changed due to the presence of the magnetic field.
As compared with the electron density Ne in the leftmost drawing
without the electromagnetic 54 (without the magnetic field), it can
be seen that in the distribution of the electron density Ne in the
case with the electromagnetic 54 (with the magnetic field)
illustrated in the other drawings, the electrons basically move in
accordance with the direction of the magnetic field illustrated in
FIG. 12. That is, in the embodiment, by forming the magnetic field
including the vertical magnetic field and the magnetic field
outwards in the diameter direction in the chamber 1 by the
electromagnetic 54, the distribution of the plasma may be
controlled to move from the center of the wafer to the outer
peripheral side thereof.
Further, as the magnetic flux density is increased, the number of
electrons following the direction of the magnetic field is
increased. Accordingly, as the magnetic flux density is increased,
the effect of further moving the distribution of the plasma to the
outer peripheral side is increased. The drawing on the rightmost
end illustrates a simulation result in the case of having the
largest magnetic flux density among the three kinds of magnetic
fields which are objects of the simulation. In this case, it can be
seen that the peak of the distribution of the electron density Ne
of plasma moves to the outermost peripheral side of the chamber
1.
Further, in the case where the electromagnet 54 is present (the
magnetic field is present), the electron temperature Te on the
wafer may be decreased as compared with the case where the magnetic
field is not present. That is, in the embodiment, by forming the
magnetic field including the vertical magnetic field and the
magnetic field outwards in the diameter direction in the chamber 1,
the temperature on the wafer disposed at the center of the chamber
1 may be suppressed from being a high temperature by using that the
electrons move outside the chamber 1. As a result, it is possible
to prevent the wafer from being damaged during plasma
processing.
FIG. 15 is a graph illustrating the electron density Ne and the
electron temperature Te of plasma at a location of 5 mm or more
spaced from the surface of the wafer based on the above simulation
result. FIG. 15A illustrates the electron density Ne for a
diameter-direction distance of the wafer. `0` of a transverse axis
represents a center location of the wafer. FIG. 15B is a graph
acquired by standardizing the electron density Ne of FIG. 15A, that
is, the electron density Ne at the center location of the wafer as
[1]. FIG. 15C illustrates the electron temperature Te for a
distance in the diameter direction of the wafer. FIG. 15D is a
graph acquired by standardizing the electron temperature Te of FIG.
15C, that is, the electron temperature Te at the center location of
the wafer as `1`.
As a result, in the embodiment, by forming the magnetic field
including the vertical magnetic field and the magnetic field
outwards in the diameter direction in the chamber 1, plasma having
more uniform electron density Ne in the diameter direction of the
wafer may be generated by increasing the electron density Ne at the
outer peripheral side of the wafer as compared with the case where
the magnetic field is not present. Further, it can be seen that in
the case of the high magnetic field of 7 G to 33 G, the electron
density Ne at the outer peripheral side of the wafer is further
increased as compared with the case of the low magnetic field of 2
G to 8 G, and as a result, the controllability of the plasma
distribution is increased.
Further, in the embodiment, by forming the magnetic field including
the vertical magnetic field and the magnetic field outwards in the
diameter direction in the chamber 1, the electron temperature Te of
the plasma is decreased as compared with the case where the
magnetic field is not present. Particularly, by forming the
electric field in the embodiment, the electron temperature Te at
the center of the wafer is decreased as compared with the case
where the magnetic field does not be present, and as a result, more
uniform plasma may be generated by the electron temperature Te in
the diameter direction of the wafer. As a result, the damage to the
wafer during the plasma processing may be decreased.
(Plasma Control by Plasma Generating Location and Magnetic
Field)
Next, a simulation how an effect on the plasma due to the magnetic
field is changed by the relationship with the plasma generating
location is performed. The result will be described with reference
to FIGS. 16 to 18. FIGS. 16 to 18 are diagrams illustrating the
electron density Ne and the electron temperature Te according to a
power output ratio from the plasma generating location by a contour
line in the second embodiment. FIG. 16 illustrates a case where the
magnetic field is not present, and FIGS. 17 and 18 illustrate a
case where the magnetic field is present. In FIG. 17, the range of
the magnetic field is 5 G to 10 G (5.times.10.sup.-4 T to 10.sup.-3
T), and in FIG. 18, the range of the magnetic field is 5 G to 20 G
(5.times.10.sup.-4 T to 2.times.10.sup.-3 T).
A percentage (%) illustrated in the drawings represents a power
output ratio. When the power output ratio is x %, power of x % is
output from the inner plasma generating location 132a, and power of
(100-x) % is output from the outer plasma generating location 132b.
For example, when the power output ratio is 100%, power of 100% is
output from the inner plasma generating location 132a. For example,
when the power output ratio is 50%, power of 50% is output from the
inner plasma generating location 132a, and power of 50% is output
from the outer plasma generating location 132b. For example, when
the power output ratio is 10%, power of 10% is output from the
inner plasma generating location 132a, and power of 90% is output
from the outer plasma generating location 132b.
When the magnetic field is not present as illustrated in FIG. 16,
since the magnetic field including the vertical magnetic field and
the magnetic field outwards in the diameter direction is not formed
in the chamber 1, the electrons do not move outside the chamber 1,
and the distribution of the electron density Ne at the center side
on the wafer is dense and the outer peripheral side is sparse. In
particular, as the power output ratio from the inner plasma
generating location 132a is high, the distribution of the electron
density Ne at the center side on the wafer is high, and as a
result, diameter-direction uniformity of the wafer
deteriorates.
Meanwhile, when the magnetic field is present as illustrated in
FIGS. 17 and 18, since the magnetic field including the
perpendicular magnetic field and the diameter-direction magnetic
field is formed in the chamber 1, the electrons move outside the
chamber 1 and the distribution of the electron density Ne in the
diameter direction of the wafer becomes more uniform. In
particular, as the power output ratio from the inner plasma
generating location 132a is low, the distribution of the electron
density Ne at the outer peripheral side on the wafer becomes high,
and as a result, diameter-direction uniformity of the wafer
increases. Meanwhile, as the power output ratio from the inner
plasma generating location 132a is high, the distribution of the
electron density Ne at the center side on the wafer becomes high,
and as a result, the diameter-direction uniformity of plasma of the
wafer decreases and the controllability of the plasma distribution
deteriorates. Further, it can be seen that since the electron
density Ne at the outer peripheral side on the wafer becomes higher
in the case of the magnetic field having magnetic flux density (5 G
to 10 G) illustrated in FIG. 17 than in the case of the magnetic
having magnetic flux density (5 G to 20 G) illustrated in FIG. 18,
the controllability of the plasma distribution is improved.
The electron density Ne of plasma above the surface of the wafer by
5 mm is illustrated by a graph of FIG. 19 and the electron
temperature Te is illustrated by a graph of FIG. 20, based on the
simulation result. FIG. 19 illustrates electron density Ne for a
diameter-direction distance of the wafer. `0` of a transverse axis
represents a center location of the wafer. FIGS. 19A and 19B
illustrate the electron density Ne in the case of the magnetic flux
density (5 G to 10 G) and FIGS. 19C and 19D illustrate the electron
density Ne in the case of the magnetic flux density (5 G to 20 G).
FIG. 19B is a graph acquired by standardizing the electron density
Ne of FIG. 19A, that is, the electron density Ne at the center
location of the wafer to `1`. FIG. 19D is a graph acquired by
standardizing the electron density Ne of FIG. 19C, that is, the
electron density Ne at the center location of the wafer to `1`.
FIG. 20 illustrates an electron temperature Te for the
diameter-direction distance of the wafer. `0` of the transverse
axis represents the center location of the wafer. FIGS. 20A and 20B
illustrate the electron temperature Te in the case of the magnetic
flux density (5 G to 10 G) and FIGS. 20C and 20D illustrate the
electron temperature Te in the case of the magnetic flux density (5
G to 20 G). FIG. 20B is a graph acquired by standardizing the
electron temperature Te of FIG. 20A, that is, the electron
temperature Te at the center location of the wafer to `1`. FIG. 20D
is a graph acquired by standardizing the electron temperature Te of
FIG. 20C, that is, the electron temperature Te at the center
location of the wafer to `1`.
According to the simulation result of the electron density Ne
illustrated in FIG. 19, in the embodiment, by forming the magnetic
field including the perpendicular magnetic field and the magnetic
field outwards in the diameter direction in the chamber 1, the
electron density Ne at the outer peripheral side of the wafer
increases and plasma having a uniform distribution of the electron
density in the diameter direction of the wafer may be generated. In
particular, the decrease in the electron density Ne at the outer
peripheral side of the wafer is less when the power output ratio is
low, that is, the power output ratio from the outer plasma
generating location is high as compared with when the power output
ratio is high, that is, the power output ratio from the outer
plasma generating location is low, and plasma having the uniform
distribution of the electron density Ne in the diameter direction
of the wafer may be generated. That is, it can be seen that when
the plasma generating location is provided at the outer peripheral
side of the wafer, the controllability of the plasma distribution
is improved. Further, it can be seen that when the magnetic field
having the magnetic flux density (5 G to 20 G) is generated rather
than the magnetic field having the magnetic flux density (5 G to 10
G), the controllability of the plasma distribution is further
improved.
Further, according to the simulation result of the electron
temperature Te illustrated in FIG. 20, in the embodiment, by
forming the magnetic field including the perpendicular magnetic
field and the magnetic field outwards in the diameter direction in
the chamber 1, the electron temperature Te decreases at the center
side of the wafer and plasma having a uniform electron temperature
Te in the diameter direction of the wafer may be generated. In
particular, the electron temperature Te at the outer peripheral
side of the wafer is further decreased when the power output ratio
is low, that is, the power output ratio from the outer plasma
generating location is high as compared with when the power output
ratio is high, that is, the power output ratio from the outer
plasma generating location is low. Further, when the magnetic field
having the magnetic flux density (5 G to 20 G) is generated rather
than the magnetic field having the magnetic flux density (5 G to 10
G), the electron temperature Te at the center side of the wafer may
be further decreased. Therefore, damage to the wafer during the
plasma processing may be further reduced.
Experiment
Control of Plasma Distribution by Magnetic Field
Next, an experiment regarding how a state of a plasma generating
area is changed by the presence or not of the electromagnet 54 and
the magnitude of a magnetic flux density was performed. In this
experiment, as illustrated in FIGS. 21A and 21B, 12 permanent
magnets 55 were placed around an outer peripheral end of the top of
a ceiling of the radial line slot antenna apparatus 100 at a
regular interval. As such, the permanent magnets 55 are provided at
the outer peripheral end side of the antenna unit 130 outside the
chamber 1 and have the S pole and the N pole, respectively, to form
a magnetic field including a vertical magnetic field, which is
illustrated in FIG. 12 and a magnetic field outwards in the
diameter direction in the chamber 1.
In the experiment, one permanent magnet 55 has a size of 20
mm.times.20 mm, but the size or shape of the permanent magnet is
not limited thereto and a magnetic field of approximately 1 G to 50
G may be applied to the lower side of the antenna unit 130 in the
chamber 1. FIG. 21C illustrates a state in which the magnetic field
of 4 G to 12 G (4.times.10.sup.-4 T to 1.2.times.10.sup.-3 T) is
applied around the electromagnet 54.
As illustrated in FIG. 21, in the radial line slot antenna
apparatus 100 according to the second embodiment in which the
experiment is performed, seven concave portions forming the plasma
generating location 132b are formed at the outer peripheral side of
the antenna unit 130 at a regular interval. However, in the case of
the locations or the number of the concave portions, when the
concave portions are formed at the location of 50% or more spaced
from the center location of the chamber 1, the number of the
concave portions is not limited to 7.
A result of experimenting on the controllability of the plasma
distribution is illustrated in FIG. 22 by using the radial line
slot antenna apparatus 100 having such a configuration. A process
condition in this case is as follows.
<Process Condition> Pressure: 20 mT (2.67 Pa) Power of
microwave: 1,700 W Frequency and power of high-frequency power
(applied from high-frequency power supply (not illustrated)
connected to susceptor: 13.56 MHz/200 W Gas type and gas flow rate:
Ar/CF.sub.4=500/100 (sccm) Ratio of gas introduced from
center/edge: 95(%)/(5%) Temperature of susceptor (electrostatic
chuck): 30.degree. C. Plasma radiation time: 60 sec.
<Experimental Result>
An upper end of FIG. 22 illustrates a result of comparing
diameter-direction etching rates of the wafer at the inner plasma
generating location 132a (plasma generating area 1) in a case where
the magnetic field is not present and in a case where the magnetic
field is present (4 G to 12 G) with each other. A lower end of FIG.
22 illustrates a result of comparing diameter-direction etching
rates of the wafer at the outer plasma generating location 132b
(plasma generating area 2) in the case where the magnetic field is
not present and in the case where the magnetic field is present (4
G to 12 G) with each other.
From the above, according to the radial line slot antenna apparatus
100 according to the embodiment, the plasma distribution in the
diameter direction of the chamber may be controlled without
increasing the electron temperature Te of plasma on the wafer.
Further, a magnetic field having comparatively low magnetic flux
density of approximately 1 G to 50 G is applied to control the
diameter-direction plasma distribution of the chamber. Accordingly,
by optimally setting a gap from the wafer to the ceiling, the
magnetic field does not reach the wafer, thereby preventing the
magnetic field from influencing the plasma processing of the
wafer.
(Dependence of Control of Plasma Distribution on Pressure)
Finally, an experimental result for the dependence of the control
of the plasma distribution on pressure will be described with
reference to FIG. 23. A process condition in this case is the same
as the process condition used in the experiment of FIG. 22, and
only a pressure value is changed to 20 mT (2.67 Pa), 30 mT (4.00
Pa), 50 mT (6.66 Pa), and 100 mT (133 Pa).
<Experimental Result>
An upper end of FIG. 23 illustrates the diameter-direction etching
rate of the wafer for each pressure in the case where the magnetic
is not present and a lower end of FIG. 23 illustrates the
diameter-direction etching rate of the wafer for each pressure in
the case where the magnetic field is present.
From the result, it can be seen that at the pressure in the chamber
which is equal to or less than 50 mT (6.66 Pa), in the case where
the magnetic is applied, the uniformity of the diameter-direction
etching rate of the chamber is increased as compared with the case
where the magnetic field is not present. In particular, the
uniformity of the etching rate at a low-pressure side at which the
pressure in the chamber is 20 mT or 30 mT is high. However, it is
considered that the uniformity of the etching rate may be enhanced
by appropriating the size or the layout of the magnetic field even
when the pressure in the chamber is approximately 100 mT.
According to the radial line slot antenna apparatus 100 according
to the second embodiment, which has been described above, the
vertical magnetic field and the transverse magnetic field outwards
in the diameter direction of the chamber 1 are applied to the
plasma generating location and an area therearound in the chamber 1
to increase the electron density Ne of plasma at the outer
peripheral side on the wafer. Therefore, the uniformity of plasma
in the diameter direction of the wafer may be increased. In
particular, in the second embodiment, a magnetic field including a
horizontal component toward the outside the chamber 1 in addition
to a vertical component is applied to lower the electron
temperature Te on the wafer as compared with the case of the first
embodiment in which the vertical magnetic field is applied.
Further, in the case of the second embodiment, the plasma
distribution may be controlled even when the gap is wide as
compared with the case of the first embodiment. As such, in the
case of the second embodiment, dependence of the gap is resolved to
control the plasma distribution with the wide gap.
Although the plasma processing apparatus and the plasma processing
method have been described by the above embodiments, the present
invention is not limited to the embodiments but various changes and
modifications can be made within the scope of the present
invention. Further, contents disclosed in the first and second
embodiments may be combined within an uncontradictory scope.
For example, as a unit for generating plasma according to the
present invention, a unit for generating microwave excitation
surface wave plasma including slot plane antenna (SPA) plasma in
addition to radial line slot antenna microwave plasma, an
inductively coupled plasma (ICP) generating unit, a remote plasma
generating unit using the generating unit and the like may be
used.
Further, in the plasma processing apparatus according to the
present invention, the slot may be provided at the location of at
least 50% or more spaced from the center location of the chamber
with respect to the radius of the chamber. That is, the slot may be
provided at only the location of 50% or more spaced from the center
location of the chamber with respect to the radius of the chamber
or both the location of 50% or less and the location of 50% or more
spaced from the center location of the chamber with respect to the
radius of the chamber.
Further, in the plasma processing apparatus according to the
present invention, the slot may be placed further outside than the
peripheral side of the object to be processed that is placed in the
susceptor or placed further outside than the inside from the
peripheral side of the object to be processed that is placed in the
susceptor by 10%.
Further, in the present invention, the object to be processed that
is subjected to the plasma processing is not limited to a
semiconductor wafer and may be, for example, a large substrate for
a flat panel display, an EL element, or a substrate for a solar
battery.
From the foregoing, it will be appreciated that various embodiments
of the present disclosure have been described herein for purposes
of illustration, and that various modifications may be made without
departing from the scope and spirit of the present disclosure.
Accordingly, the various embodiments disclosed herein are not
intended to be limiting, with the true scope and spirit being
indicated by the following claims.
* * * * *